Fundamentals of Electricity

1
Chapter 5

• Fundamentals of Electricity

2
Objectives (1 of 3)

• Define the terms electricity and electronics.
• Describe the atomic structure.
• Outline how some of the chemical and electrical
  properties of atoms are defined by the number of
  electrons in their outer shells.
• Outline the properties of conductors, insulators,
  and semiconductors.
• Describe the characteristics of static
  electricity.

3
Objectives (2 of 3)

• Define what is meant by the conventional and
  electron theories of current flow.
• Describe the characteristics of magnetism and the
  relationship between electricity and magnetism.
• Describe how electromagnetic field strength is
  measured in common electromagnetic devices.
• Define what is meant by an electrical circuit and
  the terms voltage, resistance, and current flow.

4
Objectives (3 of 3)

• Outline the components required to construct a
  typical electrical circuit.
• Perform electrical circuit calculations using
  Ohms law.
• Identify the characteristics of DC and AC.
• Describe some methods of generating a current
  flow in an electrical circuit.
• Describe and apply Kirschhoffs first and second
  laws.

5
Atomic Structure and Electron Movement (1 of 7)
6
Atomic Structure and Electron Movement (2 of 7)

• All matter is electrical in essence.
• All matter is composed of atoms.
• The atom is the smallest particle in a chemical
  element.
• The atomic structure of an element determines its
  chemical and electrical characteristics.
• The chemical and electrical properties of atoms
  are defined by the number of electrons in their
  outer shells.

7
Atomic Structure and Electron Movement (3 of 7)

• Nucleus
• In the center of every atom is a nucleus.
• Protons
• The nucleus is made up of positively charged
  matter called protons.
• Neutrons
• The nucleus contains matter with no charge
  called neutrons.
• Electrons
• Negatively charged particles called electrons are
  orbiting each atomic nucleus.

8
Atomic Structure and Electron Movement (4 of 7)

• Electrons orbit the nucleus in concentric paths
  called shells.
• All electrons are alike -- AND -- all protons are
  alike.
• So where is the difference?
• Every chemical element has a distinct identity
  and is made up of distinct atoms.
• That is, each has a different number of protons
  and electrons.

9
Atomic Structure and Electron Movement (5 of 7)

• In an electrically balanced atom, the number of
  protons equals the number of electrons.
• This means that the atom is in what is described
  as a neutral state of electrical charge.
• Ion
• An atom with either a deficit or excess of
  electrons is known as an ion.
• Charge can move from one point to another.
• Like charges repel.
• Unlike charges attract.

10
Atomic Structure and Electron Movement (6 of 7)

• Electrons (negative charge) are held in their
  orbital shells by the nucleus (positive charge)
  of the atom.
• Electrons are prevented from colliding with each
  other because they all have similar negative
  charges that tend to repel each other.
• A molecule is a chemically bonded union of two or
  more atoms.
• A compound is a chemically bonded union of atoms
  of two or more dissimilar elements.

11
Atomic Structure and Electron Movement (7 of 7)

• All atoms have an electrical charge.
• An atom is balanced when the number of protons
  match the number of electrons and is said to be
  in an electrically neutral state.
• Electricity is concerned with the behavior of
  atoms that have become unbalanced or electrified.
• Electricity may be defined as the movement of
  free electrons from one atom to another.
• Current flow is a measurement of the number of
  free electrons passing a given point in an
  electrical circuit per second.

12
Conductors and Insulators (1 of 4)

• Electron movement through a conductor is referred
  to as current.
• To produce current flow, electrons must move from
  atom to atom.

13
Conductors and Insulators (2 of 4)

• A conductor is generally a metallic element that
  contains fewer than four electrons in its outer
  shell or valence.
• Copper, aluminum, gold, silver, iron, and
  platinum are classified as conductors.

14
Conductors and Insulators (3 of 4)

• An insulator is a nonmetallic substance that
  contains five or more electrons in its outer
  shell or valence.
• Glass, mica, rubber, and plastic are good
  insulators.

15
Conductors and Insulators (4 of 4)

• Semiconductors are a group of materials that
  cannot be classified either as conductors or
  insulators.
• They have exactly four electrons in their outer
  shell.
• Silicon (Si) is an example of a semiconductor.

16
Current Flow (1 of 3)

• Conventional theory states that current flows
  from positive to negative.
• Vehicle schematics use conventional theory almost
  exclusively.

17
Current Flow (2 of 3)

• When the electron was discovered, scientists
  revised the theory of current flow and called it
  electron theory.
• The electron theory states that current flow is
  from negative to positive.

18
Current Flow (3 of 3)

• Charge differential or voltage is a measure of
  electrical pressure. It is referred to as
• Charge differential
• Voltage (V)
• Electro-motive force (EMF)
• Potential difference (PD)
• The greater the difference, the greater will be
  the rate of current flow.

19
Magnetism (1 of 3)

• A bar shaped permanent magnet has a north and a
  south pole at opposite ends.
• Like poles repel.
• Unlike poles attract.
• The lines of force surrounding the magnet are
  referred to as flux lines.

20
Magnetism (2 of 3)

• Flux lines flow in one direction.
• Flux lines exit from the magnets north pole and
  enter through the south pole.
• The flux density (concentration) determines the
  magnetic force.

21
Magnetism (3 of 3)

• The flux density is always greatest at the poles
  of a magnet.
• Flux lines do not cross each other in a permanent
  magnet.
• Flux lines facing the same direction attract.
• Flux lines facing opposite directions repel.

22
Electromagnetism (1 of 3)

• Current flow through any conductor creates a
  magnetic field.
• Magnetic lines of force do not change when the
  current flow through a conductor is constant.
• When current flow increases, the lines of force
  will extend further from the conductor.

23
Electromagnetism (2 of 3)

• The intensity and strength of magnetic lines of
  force increase proportionally with an increase in
  current flow through a conductor.
• Similarly, they decrease proportionally with a
  decrease in current flow through the conductor.

24
Electromagnetism (3 of 3)

• A rule called the right-hand rule is used to
  indicate the direction of the magnetic lines of
  force.

25
Using Electromagnetism (1 of 2)

• A magnetic field exists when current flows
  through a wire.
• When the wire is coiled, the magnetic field is
  intensified.
• When an iron core is placed in the center of this
  coil, the magnetic field is further intensified.

26
Using Electromagnetism (2 of 2)

• Magneto-motive force is measured in ampere-turns
  (at).

27
Electrical Current Characteristics (1 of 2)

• Direct current
• Current flows in one direction only.
• Current flow may be
• Continuous
• Pulsed
• DC current is used almost exclusively in highway
  vehicles.

28
Electrical Current Characteristics (2 of 2)

• Alternating current
• Current cyclically reverses at high speed.
• AC current is used in alternators and by certain
  sensors.

29
Sources of Electricity (1 of 2)

• Chemical
• In a lead acid battery, voltage is produced by a
  chemical reaction between lead and lead peroxide
  plates submersed in sulfuric acid.

30
Sources of Electricity (2 of 2)

• Static electricity
• Thermoelectric
• Photoelectric
• Piezoelectric

31
Electromagnetic Induction

• Electromagnetic induction
• Current is produced in a conductor that is moved
  through a stationary magnetic field.
• Current is produced when a magnetic field is
  moved past a stationary conductor.
• Electromagnetic induction is a means of
  converting mechanical energy into electrical
  energy.

32
Electrical Circuits and Ohms Law (1 of 5)

• Ohms law describes the relationship between
  electrical potential, current, and resistance.
• An electrical circuit must have
• Power source
• Path
• Load

33
Electrical Circuits and Ohms Law (2 of 5)

• Voltage
• Current
• Resistance
• Circuit components
• Power source
• Conductors
• Switches
• Circuit protection devices

34
Electrical Circuits and Ohms Law (3 of 5)

• Series circuits
• There is a single path for current to flow.
• All of the current flows through each resistor in
  the circuit.
• Parallel circuits
• There are multiple paths for current to flow.
• The resistance in each path determines the
  current flow through it.
• Series parallel circuits

35
Electrical Circuits and Ohms Law (4 of 5)

• Electrical circuit terminology
• Short circuit
• Open circuit
• Grounds
• Short to ground
• High resistance circuits

36
Electrical Circuits and Ohms Law (5 of 5)

• OHMS law states that an electrical pressure of 1
  volt is required to move 1 amp of current through
  a resistance of 1 ohm.
• E I x R
• I Intensity current in amps
• E EMF (electromotive force) pressure in volts
• R resistance resistance in ohms
• This is a mathematical formula that technicians
  MUST know.

37
Ohms Law Applied to Series Circuits

• All of the current flows through all of the
  resistances in the circuit
• Total circuit resistance is the sum of all of the
  resistances. Rt R1 R2 etc

38
Kirchhoffs Law of Current

• Current flowing into a junction or point in an
  electrical circuit must equal the current flowing
  out.

39
Kirchhoffs Law of Voltage Drops

• Voltage will drop in exact proportion to the
  resistance, and the sum of the voltage drops must
  equal the voltage applied to the circuit.

40
Power

• The unit for measuring power is the watt usually
  represented by the letter P.
• P I x E
• 1 horsepower (HP) 746 watts

41
Electric Motor and Generator Principle (1 of 3)
42
Electric Motor and Generator Principle (2 of 3)

• DC motors
• The electric motor converts electrical energy
  into mechanical energy.
• Current-carrying conductors are arranged as loops
  of wire in an armature.
• The armature is placed inside a magnetic field.
• When current flows through the armature, torque
  is produced.

43
Electric Motor and Generator Principle (3 of 3)

• Generators
• A generator is simply an electric motor with its
  function reversed.
• AC generators produce AC current which must be
  rectified to DC.
• Reluctor-type generators consisting of a
  permanent magnet, a coil of wire, and a toothed
  reluctor are used as shaft speed sensors.

44
Capacitance

• Capacitors store electrons.
• A capacitor consists of two conductors separated
  by an insulating material called dielectric.

45
Types of Capacitors

• Power supply filter
• Spike suppressant
• Resistor-capacitor circuits (R-C circuits)

46
Coils, Transformers, and Solenoids

• Two coils are arranged so that one is subject to
  a magnetic field created in the other.
• The input coil is the primary coil.
• The output coil is the secondary coil.
• Step-up transformers have secondary coils with a
  greater number of windings.
• Step-down transformers have secondary coils with
  a lower number of windings.

47
Solenoids and Magnetic Switches

• Magnetic switches are used so that a low current
  can control a high current.
• Solenoids use the same operating principle, but
  are used to convert electrical energy into
  mechanical movement.

48
Summary (1 of 7)

• All matter is composed of atoms.
• All atoms have an electrical charge.
• When an atom is balanced (the number of protons
  match the number of electrons), the atom can be
  described as being in an electrically neutral
  state.
• All matter is electrical in essence.
• Electricity concerns the behavior of atoms that
  have become, for whatever reason, unbalanced or
  electrified.
• Electricity may be defined as the movement of
  free electrons from one atom to another.

49
Summary (2 of 7)

• Current flow is measured by the number of free
  electrons passing a given point in an electrical
  circuit per second.
• Electrical pressure or charge differential is
  measured in volts, resistance in ohms, and
  current in amperes.
• The magnetic properties of some metals such as
  iron are due to electron motion within the atomic
  structure.
• A direct relationship exists between electricity
  and magnetism.
• Electromagnetic devices are used extensively on
  vehicles.

50
Summary (3 of 7)

• Magneto-motive force (mmf) is a measure of
  electromagnetic field strength.
• Its unit is ampere- turns (At).
• Ohms law is used to perform circuit calculations
  on series, parallel, and series-parallel
  circuits.
• In a series circuit, there is a single path for
  current flow and all of the current flows through
  each resistor in the circuit.
• A parallel circuit has multiple paths for current
  flow.
• The resistance in each path determines the
  current flow through it.

51
Summary (4 of 7)

• Kirchhoffs law of voltage drops states that the
  sum of voltage drops through resistors in a
  circuit must equal the source voltage.
• When current is flowed through a conductor, a
  magnetic field is created.
• Reluctance is resistance to the movement of
  magnetic lines of force.
• Iron cores have permeability and are used to
  reduce reluctance in electromagnetic fields.
• Capacitors are used to store electrons.
• They consist of conductor plates separated by a
  dielectric.

52
Summary (5 of 7)

• Capacitance is measured in farads.
• Capacitors are rated by voltage and by
  capacitance.
• When current is flowed through a wire conductor,
  an electromagnetic field is created.
• When the wire is wound into a coil, the
  electromagnetic field strength is intensified.
• The principle of a transformer can be summarized
  by describing it as flowing current through a
  primary coil and inducing a current flow in a
  secondary or output coil.

53
Summary (6 of 7)

• Transformers can be grouped into three
  categories isolation, step-up, and step-down.
• An electromagnetic switch is used in a truck
  electrical circuit to enable a low-current
  circuit to control a high-current circuit.
• A relay is an example of an electromagnetic
  switch.
• A solenoid uses similar operating principles to
  an electromagnetic switch except that it converts
  electromagnetic energy into mechanical movement.

54
Summary (7 of 7)

• Solenoids are used extensively in truck
  electrical circuits for functions such as starter
  engage mechanisms, diesel electronic unit
  injector control, automatic transmission clutch
  controls, and suspension pilot switches.